Rollup merge of #109435 - oli-obk:🇨🇭🥚_copy_op, r=RalfJung

Detect uninhabited types early in const eval

r? `@RalfJung`

implements https://github.com/rust-lang/rust/pull/108442#discussion_r1143003840

this is a breaking change, as some UB during const eval is now detected instead of silently being ignored. Users can see this and other UB that may cause future breakage with `-Zextra-const-ub-checks` or just by running miri on their code, which sets that flag by default.

3 files changed, 8 insertions, 7 deletions

diff --git a/compiler/rustc_const_eval/src/const_eval/machine.rs b/compiler/rustc_const_eval/src/const_eval/machine.rs
index a44f70ed059..350ce529ef5 100644
--- a/compiler/rustc_const_eval/src/const_eval/machine.rs
+++ b/compiler/rustc_const_eval/src/const_eval/machine.rs
@@ -2,7 +2,7 @@ use rustc_hir::def::DefKind;
 use rustc_hir::{LangItem, CRATE_HIR_ID};
 use rustc_middle::mir;
 use rustc_middle::mir::interpret::PointerArithmetic;
-use rustc_middle::ty::layout::FnAbiOf;
+use rustc_middle::ty::layout::{FnAbiOf, TyAndLayout};
 use rustc_middle::ty::{self, Ty, TyCtxt};
 use rustc_session::lint::builtin::INVALID_ALIGNMENT;
 use std::borrow::Borrow;
@@ -335,8 +335,8 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir,
     }
 
     #[inline(always)]
-    fn enforce_validity(ecx: &InterpCx<'mir, 'tcx, Self>) -> bool {
-        ecx.tcx.sess.opts.unstable_opts.extra_const_ub_checks
+    fn enforce_validity(ecx: &InterpCx<'mir, 'tcx, Self>, layout: TyAndLayout<'tcx>) -> bool {
+        ecx.tcx.sess.opts.unstable_opts.extra_const_ub_checks || layout.abi.is_uninhabited()
     }
 
     fn alignment_check_failed(
diff --git a/compiler/rustc_const_eval/src/interpret/machine.rs b/compiler/rustc_const_eval/src/interpret/machine.rs
index c134d3a6b2f..aca68dc454b 100644
--- a/compiler/rustc_const_eval/src/interpret/machine.rs
+++ b/compiler/rustc_const_eval/src/interpret/machine.rs
@@ -8,6 +8,7 @@ use std::hash::Hash;
 
 use rustc_ast::{InlineAsmOptions, InlineAsmTemplatePiece};
 use rustc_middle::mir;
+use rustc_middle::ty::layout::TyAndLayout;
 use rustc_middle::ty::{self, Ty, TyCtxt};
 use rustc_span::def_id::DefId;
 use rustc_target::abi::{Align, Size};
@@ -145,8 +146,8 @@ pub trait Machine<'mir, 'tcx>: Sized {
         check: CheckAlignment,
     ) -> InterpResult<'tcx, ()>;
 
-    /// Whether to enforce the validity invariant
-    fn enforce_validity(ecx: &InterpCx<'mir, 'tcx, Self>) -> bool;
+    /// Whether to enforce the validity invariant for a specific layout.
+    fn enforce_validity(ecx: &InterpCx<'mir, 'tcx, Self>, layout: TyAndLayout<'tcx>) -> bool;
 
     /// Whether function calls should be [ABI](CallAbi)-checked.
     fn enforce_abi(_ecx: &InterpCx<'mir, 'tcx, Self>) -> bool {
diff --git a/compiler/rustc_const_eval/src/interpret/place.rs b/compiler/rustc_const_eval/src/interpret/place.rs
index 3c463500a60..ff6db143ddf 100644
--- a/compiler/rustc_const_eval/src/interpret/place.rs
+++ b/compiler/rustc_const_eval/src/interpret/place.rs
@@ -461,7 +461,7 @@ where
     ) -> InterpResult<'tcx> {
         self.write_immediate_no_validate(src, dest)?;
 
-        if M::enforce_validity(self) {
+        if M::enforce_validity(self, dest.layout) {
             // Data got changed, better make sure it matches the type!
             self.validate_operand(&self.place_to_op(dest)?)?;
         }
@@ -616,7 +616,7 @@ where
     ) -> InterpResult<'tcx> {
         self.copy_op_no_validate(src, dest, allow_transmute)?;
 
-        if M::enforce_validity(self) {
+        if M::enforce_validity(self, dest.layout) {
             // Data got changed, better make sure it matches the type!
             self.validate_operand(&self.place_to_op(dest)?)?;
         }